I've long considered Wickard v. Filburn to be the worst SCOTUS decision. Perhaps it still is, based on how much widespread damage it does to this day.
That said, the Arver v. US decision takes the cake for utter incomprehensibility and circular logic.
Chief Justice White spends the entire decision discussing the legality and normalcy of national guard, conscription, etc PRIOR to the ratification of the Thirteenth Amendment, then in a brief statement at the end, can't imagine how the 13A would change any of that so it must not, DUH.
"Finally, as we are unable to conceive upon what theory the exaction by government from the citizen of the performance of his supreme and noble duty of contributing to the defense of the rights and honor of the nation as the result of a war declared by the great representative body of the people can be said to be the imposition of involuntary servitude in violation of the prohibitions of the Thirteenth Amendment, we are constrained to the conclusion that the contention to that effect is refuted by its mere statement."
I suppose if one doesn't ever actually READ the 13A and parse the words "involuntary" and "servitude" then one could torture oneself into this same conclusion. I don't actually hold out hope the current SCOTUS will reverse Arver in our lifetimes, but it's important for Americans to understand the ridiculous logic employed here to justify forcing American citizens to fight in a foreign war.